1. Field of Invention
The present invention relates to hoisting and handling systems and methods. More particularly, the present invention relates to a system and method to facilitate the hoisting, positioning, installation and removal of continuous track drive units.
2. Description of Prior Art
Continuous track drive units are used in many types of vehicles and machinery including tractors, construction equipment, and military vehicles. Because continuous track drive units have no beginning or end, installation is often difficult and cumbersome given the need for precise positioning and alignment with respect to the vehicle hubs. Furthermore, because continuous drive track units are not stretchable, the continuous track drive unit must be held taut and in a configuration nearly identical to that of an installed track prior to installation. Such requirements add greatly to the difficulty in installing and removing continuous track drive units.
Another consideration is the weight of the continuous track drive unit. Often, track drive units are constructed with closely spaced steel cables running parallel to the circumference. The steel cables are sheathed in a cast tread, while rubber cogs are cast into the inside circumference to keep the continuous track drive unit captive and centered on its support and drive idlers. These components render continuous track drive units heavy and awkward to manipulate. Nonetheless, these limitations must be overcome when continuous track drive units are installed on vehicles.
Continuous track drive units are commonly shipped positioned on their sides in closely fitted crates. It is advantageous to remove the continuous track drive unit without damage to the unit itself or to the crate. However, using presently available methods, removal of the continuous track drive unit is typically accomplished using multiple chains or wire rope or synthetic slings, and considerable physical strain is required to position these around the track, before it can be lifted from its crate with a suitable hoist. Tong style gripping clamps may also be used to grip the track, thereby eliminating the strain of manipulating the track over chain or sling rigging. Because the purpose of this style clamp serves is very specialized, these clamps are not readily available in the field. Furthermore, the balancing of stresses applied to multiple clamps by the manner in which they are rigged to the hoisting device is easily misjudged, increasing the risk of damaging the track. A method is clearly needed, which this invention provides, to securely and quickly lift the continuous track drive unit from its crate, to even begin dealing with it, that offers no potential injury to the operator, the track or its shipping crate.
Indeed, because continuous track drive units are so heavy, they can be damaged by their own weight if they are lifted improperly. Improper lifting can give rise to a stress point, and ultimately a stress concentration factor, at the point where the continuous track drive units are lifted. Furthermore, internal damage to the continuous track drive units can occur which are not visible to the eye, thereby creating further problems.
By far the greatest difficulty in handling continuous track drive units is during the installation of the track to a vehicle. Presently, rigging used to support and maneuver continuous track drive units is often inadequate because overhead clearance at multiple lift points is obstructed by the vehicle's superstructure and other objects. Further, because vehicle track frames can be displaced only to a small increment, the continuous track drive unit must be installed in a nearly taut position prior to being placed over the idlers. Because there is no single point of balance and no inherent ability to stretch a track over the machine idlers, much time and effort is lost in attempting to lever the track onto the idlers, and the risk of injury to the operators is greatly increased. Further, such methods do not control sagging of the continuous track drive unit which binds and drags on every surface with which it comes in contact.
Yet another problem occurs when continuous track drive units are removed from the vehicle idlers. In order to facilitate removal, vehicle idlers can be displaced somewhat in order to loosen the tension of the track. The end idlers are composed of an inner and outer half, separated by a gap in which the cogs that are integrated into the inner surface of the track run captive, preventing lateral movement of the track on these idlers. The outer end idler halves are removed from the vehicle in order to free the track cogs during removal of the continuous track drive unit. Nonetheless, the weight of the track on the idlers often resists removal. Furthermore, at this point, it is difficult, to near impossible, to attach rigging to support the track such as chain, band slings, forklift tines or gripping clamps. Therefore, at that phase of removal, the track must be pulled and pried off the machine idlers by workers, thereby slowing down and complicating the process, to say nothing of the potential for human injury.
In view of the foregoing, there is a need for a method that overcomes the deficiencies in the prior art.